嗨，我正在处理一个从数据库读取大量数据的文件。然后我在nodejs中使用一个名为json2csv的模块来转换数据集并将其写入csv文件。这是 json2csv 模块的链接。 https://www.npmjs.com/package/json2csv 使用此模块，它将数据转换为 csv 数据，但我遇到的问题是，当它开始写入文件时，由于数据集太大，它会耗尽内存并崩溃。有什么方法可以写入一小块数据而不是写入全部数据？这是我到目前为止所拥有的。

    /*require the ibm_db module*/ 
var ibmdb = require('ibm_db'); 
var fs    = require("fs"); 
var json2csv = require('json2csv'); 
var db2query = "SELECT DISTINCT DISCEVNT.EVENT_RUNID, DISCEVNT.EVENT_TIME, DISCEVNT.EVENT_SEVERITY, DISCEVNT.EVENT_ATTRIBUTE, DISCEVNT.EVENT_DESC, DISCEVNT_ATTR_IP.DE_IP, DISCEVNT_ATTR_IP.DE_HOSTNAME, DISCEVNT_ATTR_IP.DE_FQDN, DISCRUN.SERVERID_X FROM (DB2INST2.DISCEVNT DISCEVNT INNER JOIN DB2INST2.DISCRUN DISCRUN ON (DISCEVNT.EVENT_RUNID = DISCRUN.DISCOVERRUNID_X)) INNER JOIN DB2INST2.DISCEVNT_ATTR_IP DISCEVNT_ATTR_IP ON (DISCEVNT_ATTR_IP.DE_ATTR = DISCEVNT.EVENT_ATTRIBUTE) WHERE (DISCEVNT.EVENT_RUNID BETWEEN 2017071400000000 AND 2017071900000000) ORDER BY DISCEVNT.EVENT_TIME ASC;"; 
var db2setup = "DRIVER={DB2};DATABASE=CMDB;UID=user;PWD=password!;HOSTNAME=localhost;port=3000"; 
var dataJson = []; 
var fields = ['EVENT_RUNID','EVENT_TIME','EVENT_SEVERITY','EVENT_ATTRIBUTE','EVENT_DESC','DE_IP','DE_HOSTNAME','DE_FQDN','SERVERID_X']; 
console.log("Test program to access DB2 sample database"); 
 
/*Connect to the database server 
  param 1: The DSN string which has the details of database name to connect to, user id, password, hostname, portnumber 
  param 2: The Callback function to execute when connection attempt to the specified database is completed 
*/ 
function getData(values){ 
    dataJson = values; 
    console.log(dataJson); 
    var csv = json2csv({ data: dataJson, fields: fields }); 
    console.log("CSV data:"); 
    console.log(csv[0]); 
    console.log(csv.length); 
    console.log(dataJson.length); 
    console.log(dataJson[0]); 
    fs.writeFile('C:\\Users\\ztaddmusr\\Desktop\\CSV FILES\\file.csv', csv, function(err) { 
      if (err) throw err; 
      console.log('file saved'); 
    }); 
 
  } 
 
ibmdb.open(db2setup, function(err, conn) 
{ 
        if(err) { 
        /* 
          On error in connection, log the error message on console 
        */ 
            console.error("error: ", err.message); 
        } else { 
 
        /* 
            On successful connection issue the SQL query by calling the query() function on Database 
            param 1: The SQL query to be issued 
            param 2: The callback function to execute when the database server responds 
        */ 
        conn.query(db2query, function(err, data) { 
 
        if(err) { 
        /* 
          On error in connection, log the error message on console 
        */ 
            console.error("error: ", err.message); 
        } else { 
            //console.log(data); 
 
            getData(data); 
            console.log('Data finished retrieving from the datatbase. Now will write to file.') 
 
        } 
            /* 
                Close the connection to the database 
                param 1: The callback function to execute on completion of close function. 
            */ 
            conn.close(function(){ 
                console.log("Connection Closed"); 
            }); 
        }); 
    } 
}); 
//var csv = json2csv({ data: dataJson, fields: fields }); 
//console.log(csv); 
//fs.writeFile('file.csv', csv, function(err) { 
//  if (err) throw err; 
//  console.log('file saved'); 
//}); 

我一直在尝试使用循环，但总是搞砸。预先感谢您的帮助!

请您参考如下方法:

如果将 ES6 与 co(npm package) 等实现一起使用，则可以使用生成器。然后您可以根据分区停止异步代码的执行，并使用 block 追加到文件。

类似这样的东西(还没有编译；可能有错误):

function* writeToCsv(csvObj){ 
  let chunkedArr = chunkify(csvObj); 
  chunkedArr.forEach(co.wrap(chunk => { 
    co.wrap(writeChunkToCsv(chunk))(dir)   
  })) 
} 
 
function* writeChunkToCsv(chunk){ 
  return dir => { 
    yield fs.writeFile(dir, csv); 
  } 
} 
 
function chunkify(arr, partitions){  
  let ansArr = []; 
  for(let i = 0, currentArr = []; i < arr.length; i++){ 
    if(i%(arr.length/partitions) === 0 || i === arr.length){ 
      ansArr = ansArr.push([...currentArr]); 
      currentArr = []; 
    } 
    else{ 
      currentArr.push(arr[i]); 
    } 
  } 
  return ansArr; 
}